In editing films in the motion picture industry, it is common practice to join separately shot scenes together by copying an intermediate negative or printing a positive using a "fade and dissolve" technique. In a fade and dissolve, a first scene is "faded out" during copying or printing thereof by progressively lightening the scene images over a series of film frames while the second scene is "dissolved in" during copying or printing thereof by progressively darkening the scene images over a series of film frames, the two copied or printed series of faded out and dissolved in film frames being superimposed on a light sensitive recording element to form a resulting fade and dissolve scene change. The fade and dissolve can be performed during the production of an intermediate negative film produced from two original negative records, or it can be accomplished as a two exposure procedure on the final positive print material stock which is projected in a movie theatre.
Copying of an original negative record to make an intermediate negative, or printing of an intermediate negative record to give a positive is accomplished in a motion picture printer by illuminating the record to be copied with a lamp through an exposing slit so that radiation passing thru the record to be copied impinges on the light sensitive material in which the reproduction will be formed as the record to be copied and the light sensitive material are together passed by the exposing slit. In a fade and dissolve, the light sensitive material is conventionally subjected to two superimposed exposures wherein the light intensity is ramped down for one scene (the faded scene) and ramped up for the other (the dissolved scene), so the total illumination (i.e., the summation of the two exposures) remains essentially constant.
It is common practice to employ as the source of illumination an additive lamp house which supplies three separate portions of the visible spectrum; one which has its peak in the blue region of the spectrum, between about 400 and 500 nm, one which has its peak in the green region of the visible spectrum between about 500 and 600 nm, and one which has its peak in the red region of the visible spectrum between about 600 and 700 nm. The exposing radiation is conventionally provided by a single white light source which is split into three separate beams which are filtered with red, green or blue filters before they illuminate the record being copied. Typically each of the exposure sources, the dyes which provide the absorption in the record to be copied and the sensitivity of the light sensitive element onto which the copy is made are chosen so that their peaks approximately match.
FIG. 1 schematically illustrates the optical system of a conventional motion picture printer comprising a lamp house 10 having lamp 11, reflector 12, condensing lenses 13 and 14 and heat filter 15; a fader 20 having a fader slit opening 21 of variable width formed between opaque elements 22a and 22b (at least one of which is movable relative to the other); dichroic filters 31a, 31b, 31c, 31d, 31e and 31f; red light valve 32a, green light valve 32b and blue light valve 32c, which modulate individual red, green and blue channel intensities; focusing lenses 33a, 33b, 33c and 33d; condensing lenses 34a, 34b and 34c; filter holder 35; and exposing slit 40, which is conventionally transversly aligned with the direction of film transport past the exposing slit. Film 50 comprising color record scenes and light sensitive material film 60 are also schematically depicted passing by exposing slit 40. A representative mechanical aperture for an exposing slit is 0.234 inch, while a representative optical aperature is 0.187 inch (i.e., the focussed width of the exposing light at the plane of the exposing slit).
Various types of filters have been used with printers to modify reproductions. Hehn U.S. Pat. No. 3,085,468 describes the use of dichroic filters in printing photographic originals in place of the red, green and blue filters commonly used in additive printing systems. Krause U.S. Pat. No. 4,359,280 describes the use of dichroic filters, and other narrow band filters to modify contrast by shifting peak intensity characteristics of the light modulated by the record being copied. Uniform wide band filters, such as Kodak Gelatine Filters, Wratten filters and custom filters made from organic or inorganic dyestuffs are also conventionally used to modify exposing light compositions for various printing purposes.
To control the illumination during the fade and dissolve exposures, motion picture printers conventionally include a "fader" which controls the intensity of the light passing into the red, green and blue filter areas of the printer. Such a fader is illustrated at 20 in FIG. 1. The optics of a motion picture printer are conventionally designed to image the fader slit edges in its open position at the plane of the final exposing slit of the printer as illustrated at 40 in FIG. 1. As the fader slit opening is closed, the width of the slit imaged onto the final exposing slit is narrowed and the intensity of light received by a film frame passing thereover at a constant rate is therefore reduced. A combination of factors can influence the summation of the two exposures generated in a photosensitive material in a fade and dissolve procedure, including: the preprogrammed exposure profile of the fader in a motion picture printer; the time between the two exposures (latent image keeping); mechanical and optical properties of the printer; and properties of the photosensitive material.
While fade and dissolve exposures are conventionally programmed so that the sum of the exposures remains constant throughout the fade and dissolve in order to avoid overall image density changes, it has been found that certain photosensitive materials, such as many commercially available motion picture print stocks, may record two separate superimposed exposures such that there is an effective speed change in one or more of the sensitive layers relative to a single exposure of equivalent intensity. Such speed changes, along with the above mentioned factors, can result in objectional color shifts or image density changes in the resulting recorded image which are evident to a viewer of a fade and dissolve transition scene. It would be desirous to be able to correct for such speed changes without having to adjust the programmed exposure profile of the printer's fader or the mechanics and optics of the printer. Further, it would additionally be desirous to control the density profile or color balance during the fade and dissolve process for artistic considerations without resorting to such adjustments.